Oxygen sensor

A sensor structure which reduces the resistance of insertion in the course of insertion of a metallic terminal member into the hollow portion of an oxygen detection element so as to enable smooth assembly and such that portions of the metallic terminal member become less susceptible to plastic deformation. An attachment portion 23c of a metallic terminal member 23 is in contact with the inner wall surface of a hollow portion 2a of an oxygen detection element 2, directly or indirectly via another member, at opposite sides thereof located along the direction of contact. Also, a gap is formed between an attachment portion 23c and the inner wall surface at opposite sides of the attachment portion 23c located along the direction of gap formation. Thus, in the course of insertion of the metallic terminal member 23 into the hollow portion 2a of the oxygen detection element 2, the resistance of insertion decreases, whereby assembly can be performed smoothly, and portions of the metallic terminal member 23 become less susceptible to plastic deformation, such as crushing, bending, or buckling.